Method for controlling the operating voltage of a fan in electrical equipment

ABSTRACT

In order to control the operating voltage of a fan in electrical equipment, the temperature of an output diode (D) of an output circuit of the power supply of the electrical equipment is monitored. The operating voltage of the fan is controlled as a function of the component temperature of this physical element such that up to a limit temperature, which is in the region of the maximum permissible component temperature of a physical element which absolutely becomes the hottest, the operating voltage of the fan is regulated at a constant, minimum level. The operating voltage is then regulated to rise continuously and rapidly up to a maximum operating voltage at which, although the component temperature of the physical element which absolutely becomes the hottest is still above the limit temperature, it is below the maximum permissible component temperature of this physical element, however.

BACKGROUND OF THE INVENTION

The invention relates to a method for controlling the operating voltageof a fan in electrical equipment.

For a power supply with fan cooling, a fan is frequently used whoserotation speed is controlled for noise reduction. Particularly in aquiet office environment, the fan noise using conventionaltemperature/rotation-speed control is nevertheless considered to be tooloud in this case. When reducing the fan rotation speed, care must betaken to ensure that the electronic physical elements which are to beprotected remain below the maximum permissible component temperaturethroughout the entire load and temperature range.

According to a previously known method, the air temperature of the powersupply is converted into a control voltage for the fan with the aid of apower stage and a temperature-dependent physical element, for exampleusing a so-called NTC or PTC thermistor, that is to say a resistor whoseresistance becomes correspondingly greater when it is cooled down orheated up, respectively. The temperature/voltage characteristic which isused in this case is at the same time relatively flat or broad, that isto say the control voltage rises in a wide range, for example between20° Celsius and 60° Celsius, from a basic voltage level to the maximumfan voltage.

In the case of some fan controllers, the temperature sensor is mountedon a heat sink of power components in the power supply so that theoutput power of the power supply is also taken into account when settingthe fan operating voltage.

U.S. Pat. No. 5,197,858 discloses a temperature-controlled speedadjustment of fans in electrical equipment, which adjustment carries outthe control of the fan in such a manner that the fan rotation speed isset to be constant at a first value up to a first equipment temperaturelimit. After this, the fan rotation speed is continuously increased upto a second equipment temperature limit. Above the second equipmenttemperature limit, the fan rotation speed remains constant.

In this context, a circuit arrangement is admittedly specified in whichthe respective equipment temperature limits can be adjusted betweenwhich the continuous rise in the fan rotation speed is intended to takeplace. However, only the principle is in fact specified as to howregulation of the fan rotation speed is intended to be carried out. Theregulation of the fan rotation speed is admittedly related to areduction in the fan noise. However, no proposal is made as to how thefan noise can be reduced to the maximum extent while maintaining thecooling function for an associated electrical equipment.

“PC-Lüfterregler” (PC fan regulators) by Svenkerud/Kristiansen in DE-Z“Elektor” (Elector), Issue 7-8/92, page 22 discloses a circuitarrangement for controlling the fan RPM of a fan in an electricalapparatus, which, besides a start-up controlling, carries out a fan RPMcontrolling, such that after the fan is started up, the fan RPM iscontrolled continuously with an increasing temperature in the electricalapparatus. For this purpose, an inception point and an increase functionfor the controlling are defined. The inception point is at 2° C. and theincreasing is determined such that the fan RPM increases continually asthe temperature increases up to a temperature of 30° C. The basis forthe controlling is the air temperature in the electrical apparatus,which the control range of 2° C. through 30° C. matches. With theproposed air controlling, a noise reduction is achieved, however, thenoise reduction does not correspond to the noise reduction that could bemaximally achieved

SUMMARY OF THE INVENTION

An object of the invention is to specify a method for controlling theoperating voltage of a fan in electrical equipment, by means of whichmethod a maximum noise reduction in the fan is achieved in a cheapmanner while maintaining required cooling performance.

In general terms the present invention is a method for controlling theoperating voltage of a fan in an electrical equipment for coolingelectrical physical elements used in the electrical equipment. Thephysical elements can assume a component temperature to above a maximumpermissible operating temperature as a function of an instantaneouspower and an ambient temperature. The temperature of an output diode ofan output circuit of the power supply of the electrical equipment ismonitored. The operating voltage of the fan is controlled as a functionof the component temperature of this output diode such that up to alimit temperature which is in the region of the maximum permissiblecomponent temperature of a physical element which absolutely becomes thehottest in the electrical equipment. The operating voltage of the fan isregulated at a constant, minimum level. The operating voltage is thenregulated to rise continuously and rapidly as a function of thetemperature up to an operating voltage at which the increase in the fanrotation speed associated therewith still ensures that, although thecomponent temperature of the physical element which absolutely becomesthe hottest is still above the limit temperature, it is below themaximum permissible component temperature of this physical element.

In an advantageous development of the present invention a higherstarting voltage is used for starting the fan than the minimum operatingvoltage of the fan after starting.

According to this, the fan is always operated at an operating voltagewhich is as low as possible. This is achieved by the following points.

A physical element in the power supply is used as the reference physicalelement for the determination of a temperature at which regulation isintended to take place, since this results in physical elements whosetemperature responses correspond in a very highly proportional manner tothe equipment power and thus make it possible to deduce how hot otherphysical elements in the equipment will become, in detail. On thisbasis, it is not necessary to monitor other temperature-criticalphysical elements in addition, even if this could still be done, inaddition, directly. It is necessary only to determine the relationshipbetween the reference physical element and a respective other physicalelement and then to set the regulation of the temperature of thereference physical element in such a manner that the maximum operatingtemperature of a respectively desired other physical element is alsotaken into account.

The output diode of an output circuit of the power supply with thegreatest power to be emitted is used, in particular, since thiscomponent is one of the physical elements which becomes the hottest and,in addition, this component is as a rule already mounted on a heat sinkso that its temperature response is correspondingly slow and atemperature sensor can very easily be provided.

As a result of the control of the fan according to the invention, therotation speed of the fan is not accelerated until extremely late andthen in all cases only to the extent that sufficient cooling is juststill provided.

Electrical equipment, such as a personal computer, is composed of a maincomponent or processor and a power supply. A fan is located in the powersupply. The fan produces an air-flow in the electrical equipment. In atypical embodiment air at a first temperature enters the main componentby a slot in the side of a case of the electrical equipment. The airthat emerges from the main component at a second temperature then entersthe power supply. The air which enters the power supply at the secondtemperature is measured in the power supply either by a temperaturedependent thyristor having a positive temperature coefficient or by atemperature dependent thyristor having a negative temperaturecoefficient. The operating voltage of the fan is regulated as a functionof the measured air temperature. The air in the power supply is thenblown out of the power supply by the fan. This draws further fresh airinto the main component. This is the typical operation in the prior art.

The operating voltage of the fan is controlled in accordance with broadcharacteristics. The operating voltage is a function of the airtemperature in the prior art devices, and the fan rotates at a basicrotational speed for a first air temperature. As the air temperatureincreases up to a second air temperature the rotation of the fan isincreased up to a maximum operating voltage for the predeterminedmaximum second air temperature. The fan rotates at its maximumrotational speed at the maximum operating voltage of the fan.

According to the present invention however, the temperature foreffecting the operating voltage of the fan is no longer determined usingthe air temperature within the power supply, but is determined using aheat sink temperature of a heat sink, for example, for an output diode.The temperature dependent thyristors are arranged on the heat sink ofthe diode for measuring the temperature of the output diode.

The operating voltage of the fan for the present invention is determinedaccording to a predetermined characteristic. According to thepredetermined characteristic, the operating voltage of the fan remainsconstant at a basic fan voltage up to a first heat sink temperature. Thefirst heat sink temperature represents a limit temperature. Above thelimit temperature, the operating voltage of the fan rises continuouslyand rapidly. At a higher, second heat sink temperature, the fan voltageis at a maximum for a maximum operation of a fan. The second heat sinktemperature is selected such that all physical elements in theelectrical equipment are still below a maximum permissible operatingtemperature.

In a simple case, the control for the fan is converted into temperatureregulation, which is produced by the fan, of the main heat sink in thepower supply. In this case, ventilation of the electrical equipment isbased on limiting a component temperature of a hottest (electrical orelectronic) physical element to a predetermined maximum value which isbelow a temperature value which would damage the other physicalelements. For example, a temperature of 100° C. is normal. The physicalelements may be both in a load and in a power supply. In the example ofa first computer, this may be a microprocessor, as well as, a 5 voltoutput diode in the power supply. In some embodiments and operation, theoutput diode will be hotter than the microprocessor, and in othersituations the microprocessor will be hotter than the output diode. Whencost and complexity are not an issue, each critical physical elementcould be monitored individually with a temperature sensor. In this case,the temperature of the hottest physical element determines the voltagefor the fan. The lowest rotational speed for the fan results from thelowest permissible operating voltage of the fan at which the fan stilloperates reliably. In order to achieve the minimum possible rotationalspeed over the entire load range of the fan, this lowest fan rotationalspeed is still maintained as the component temperature rises. The fanvoltage does not start to rise until a first limit temperature isexceeded. The rise in the temperature/voltage characteristic isrelatively steep. The maximum fan voltage is reached at an upper secondheat sink temperature which, for tolerance reasons, is somewhat belowthe maximum component temperature. This form of temperature/voltagecharacteristic is the minimum possible rotational speed of the fan at alow load, while the minimum necessary rotation of the fan is set at ahigher load in order to operate the hottest physical element within asafety margin which is below a maximum temperature of the hottestphysical element. The temperature response of the hottest physicalelement is taken into consideration, and this corresponds to thetemperature regulation of this physical element via the fan rotationalspeed.

In a first advantageous development of the present invention, and inorder to reduce cost and complexity, the number of temperature sensorscan be reduced to a single sensor which is thermally connected to theheat sink of the 5 volt output diode in the power supply. In most cases,this is the hottest physical element in the power supply. It is nowdetermined by measurements in the entire system at various upgradelevels, load levels, and outside temperatures, whether there is anyphysical element in the load which exceeds its working temperature rangewith this regulation. If this is the case, the first and secondtemperature limits must be appropriately reduced until all the physicalelements remain below their maximum temperatures in all operatingconditions. In order to reduce the lowest operating voltage for the fanstill further, the operating voltage of the fan can be briefly increasedduring starting, in order that it starts reliably. The lowestpermissible operating voltage which is set after this can be lower,since the starting of the fan normally requires more voltage than theoperation after starting at a constant rotational speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIG. 1 shows an outline illustration of an electrical equipment havingfan control in accordance with a known type,

FIG. 2 shows a temperature regulation response of the electricalequipment according to FIG. 1,

FIG. 3 shows an outline illustration of an electrical equipment havingfan control according to the invention, and

FIG. 4 shows a temperature regulation response of the electricalequipment according to FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an electrical equipment which is composed of a maincomponent PC and a power supply SV. Such equipment may be, for example,a personal computer.

A fan L is arranged in the power supply SV. The fan L produces an airflow in the electrical equipment, which air flow is indicated by arrows.In this case, air at the temperature TL enters the main component PC viaslots at the side. The air then emerges from the main component PC atthe temperature TPCL and enters the power supply SV. The air whichenters the power supply SV at the temperature TPCL is then measured inthe power supply SV either by a temperature-dependent thermistor havinga positive temperature coefficient PTC or by a temperature-dependentthermistor having a negative temperature coefficient. The operatingvoltage of the fan is regulated as a function of the measured airtemperature. The air in the power supply is then blown out of the powersupply by the fan. The suction draws fresh air into the main componentPC.

The operating voltage of the fan L is controlled in accordance with abroad characteristic, as is shown in FIG. 2. In the case of an airtemperature TPCL1, a voltage ULnorm is produced for the fan L, at whichvoltage the fan L rotates at a basic rotation speed. Up to an airtemperature of TPCL2, which corresponds to a maximum permissibletemperature at which it is assumed that all the physical elements in theelectrical equipment are still operating correctly, the fan voltage ULis increased up to a level ULmax. The fan rotates at its maximumrotation speed at the maximum fan voltage ULmax.

The situation which is illustrated in FIGS. 1 and 2 represents a priorart. The situation which is shown in FIGS. 3 and 4 represents a solutionaccording to the invention.

FIG. 3 shows the same electrical equipment as that in FIG. 1, but withthe difference that the temperature for producing a fan voltage UL is nolonger determined using the air temperature within the power supply SVbut using the heat sink temperature TK of the heat sink for an outputdiode D. The temperature-dependent thermistors PTC and NTC,respectively, are arranged on the heat sink of the diode D for thispurpose.

The determination of the fan voltage UL is in this case carried out inaccordance with the characteristic indicated in FIG. 4. According to thecharacteristic, the fan voltage remains constant at a basic fan voltageULnorm up to a first heat sink temperature TK1. The first heat sinktemperature TK1 represents a limit temperature. Above the limittemperature TK1, the fan voltage UL rises continuously and rapidly. At ahigher, second heat sink temperature TK2, the fan voltage UL is at amaximum, at a value ULmax. The second heat sink temperature TK2 isselected in such a manner that all the physical elements in theelectrical equipment are still below the maximum permissible operatingtemperature. The limit temperature TK1 is established in the region ofthe second heat sink temperature TK2.

There now follows a general description of the situation illustrated inFIGS. 3 and 4.

It is to be understood that the electrical apparatus depicted in FIG. 3is the same electrical apparatus as is depicted in FIG. 1. It is thusclear that, first, the object identified as element D in FIG. 1 is anoutput diode, and second, that the output diode D is the same outputdiode used in FIG. 3.

In the simplest case, the control for the fan L is converted intotemperature regulation, which is produced by the fan, of the main heatsink in the power supply SV. In this case, one starts from the followingconsideration: the ventilation of an electrical equipment is based onlimiting the component temperature of the hottest (electrical orelectronic) physical element to a predetermined maximum value which isbelow the respective destruction limit. A temperature of 100° Celsius isnormal, for example. The physical elements in question may be both inthe load and in the power supply. In the example of a personal computer,this may be a microprocessor MP and, at the same time, a 5-volt outputdiode D in the power supply. Depending on the upgrade level and the loadlevel, the output diode D will be hotter, on the one hand, in this case,and the micro-processor MP will be hotter in another load case. If costand complexity play only a minor role, each critical physical elementcan be monitored individually with a temperature sensor. In this case,the temperature of the hottest physical element determines the voltagefor the fan L. The lowest rotation speed for the fan L results from thelowest permissible operating voltage ULnorm of the fan L at which thefan still starts reliably. In order now to achieve the minimum possiblerotation speed over the entire load range for the fan L, this lowest fanrotation speed is still maintained as the component temperature rises.The fan voltage UL does not start to rise until a limit temperature TK1is exceeded. The rise in the temperature/voltage characteristic isrelatively steep (considerably steeper than, for example, thecharacteristic illustrated in FIG. 2). The maximum fan voltage ULmax isreached at an upper heat sink temperature TK2 which, for tolerancereasons, is somewhat below the maximum component temperature. This formof temperature/voltage characteristic gives the minimum possiblerotation speed of the fan L at low load, while the minimum necessaryrotation speed of the fan is set at higher load in order to operate thehottest physical element with a safety margin below its maximumtemperature. If the temperature response of the hottest physical elementis considered, this corresponds to a temperature regulation of thisphysical element via the fan rotation speed.

Two advantageous refinements are conceivable: in order to reduce costsand complexity, the number of temperature sensors can be reduced to asingle sensor which is thermally connected to the heat sink of the5-volt output diode D in the power supply SV. In most cases, this is thehottest physical element in the power supply SV. It is now necessary todetermine by measurements in the entire system at various upgradelevels, load levels and outside temperatures whether there is anyphysical element in the load which exceeds its working temperature rangewith this regulation. If this is the case, the two temperature limitsTK1 and TK2 must be appropriately reduced until all the physicalelements remain below their maximum temperatures in all operatingconditions. In order to reduce the lowest operating voltage ULnorm forthe fan still further, the operating voltage of the fan L can be brieflyincreased during starting, in order that it starts reliably. The lowestpermissible operating voltage which is set after this can be lower,since the starting of the fan L normally requires more voltage than theoperation after starting at a constant rotation speed.

The invention is not limited to the particular details of the methoddepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described method withoutdeparting from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method for controlling an operating voltage ofa fan in an electrical equipment for cooling electrical physicalelements used in the electrical equipment, comprising the steps of:monitoring a temperature of an output diode, the temperature of theoutput diode being indicative of the greatest power of an output circuitof a power supply of the electrical equipment, said output diode havinga temperature response corresponding to power being fed by the powersupply to the electrical equipment so that its temperature is thusrelated to how hot other physical elements in the equipment will become;controlling an operating voltage of the fan as a function of thetemperature of the output diode; and the operating voltage of the fanbeing controlled such that the operating voltage of the fan is firstregulated at a constant minimum level until a first temperature isreached by the output diode at which time the operating voltage of thefan is regulated to rise continuously as a function of the output diodetemperature until a second higher output diode temperature is reached atwhich the fan voltage is at a maximum, the second temperature beingselected such that all physical elements in the electrical equipmentincluding the output diode are still below a maximum permissibleoperating temperature.
 2. The method according to claim 1 wherein theoutput diode temperature comprises a temperature of a heat sink to whichthe output diode is connected.
 3. The method according to claim 1wherein the fan rotates at its maximum rotation speed at said maximumfan voltage.
 4. The method according to claim 1 wherein a startingvoltage is used for starting the fan which is higher than said minimumoperating voltage of the fan after starting.